Why did the US and Britain create joint operations in response to Germany's lebensraum and how did Secretary of War Harry Stimson Shift focus for Japan? Please please help

Germany’s lebenstraum was an attempt to colonize Germans toward Eastern Europe. To accomplish this the Germans followed their version of Manifest Destiny which meant that to migrate east, Germany’s citizens must replace those deemed, by the German interpretation of Darwinism, as inferior. The Jews were the people thought to be inferior. He US and Britain joined forces lebenstraum because the US was dragged into the fight with Britain against Germany’s incursion east. Sec of War Simpson used the invasion of Pearl Harbor to shift focus to Japan.